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This paper discusses power-system instability and the importance of fast fault-clearing performance to aid in reliable production of power. An explanation regarding small-signal stability, high-impedance transmission lines, line loading, and high-gain fast-acting excitation systems is provided. Transient stability is discussed, including synchronizing and damping torques. The power-angle curve is used to illustrate how fault-clearing time and high initial response excitation systems can affect transient stability. The term "power-system stability" has become increasingly popular in generation and transmission. The sudden requirement for power-system stabilizers (PSSs) has created confusion about their applicability, purpose, and benefit to the system. This paper discusses the fundamentals of the PSS and its effectiveness. In today's paper industry, PSSs are being applied on larger machines in the northwest United States and Canada. [ABSTRACT FROM AUTHOR]

System reliability is an integral part of a properly designed deregulated electricity market, even though wholesale energy prices are its most visible piece. This paper discusses the resources, collectively known as the ancillary, services, in a power system for maintaining reliability. It then discusses an integrated approach in systematically determining and securing the needed ancillary services and system configuration across multiple time spans, culminating in the cooptimization of energy and ancillary services for security-constrained generator unit commitment in the day-ahead market and security-constrained economic dispatch of the generators in real-time operation. The paper also provides a summary of the ancillary services market in several U.S. power markets and proposes several technical issues for further discussion and research. [ABSTRACT FROM AUTHOR]

The evaluation of locational marginal prices or LMPs, which constitute the basis of the new generation of market design in the U.S., is a critical need in the side-by-side operation of electricity markets and power systems. Their use in various applications such as congestion management and hedging requires specific LMP components in the computations. We provide a general formulation for the evaluation of the LMP components by making explicit use of the important role played by the nodes with generators with free capacity. On the other hand, the LMPs of the nodes without generation or with the generators at their limits are a function of the LMPs at the marginal nodes and the impacts of the network constraints, including the losses in the network. In the formulation, we pay special attention to the importance of the assumptions and specifications—the so-called policy specification—in the determination of the components. We obtain a very general formulation that brings under a single framework the different decomposition approaches that exist. The formulation's comprehensiveness brings numerous insights into the various decompositions, provides a platform for their comparative analysis, and allows us to understand the direct implications and the role of the policy specified. Moreover, the formulation reveals the limitations of any decomposition into the components due to the underlying structural interdependencies among them, which is clearly shown in this paper. We provide an example to illustrate the capabilities and the insights obtainable with the use of this formulation. [ABSTRACT FROM AUTHOR]

Utilities have long struggled with establishing re- source planning criteria that ensure adequate resources to meet loads at low cost. Historically, many utilities used planning reserve margin criteria. The onset of deregulation brought about a paradigm shift in which it was expected that markets would provide a more efficient mechanism for maintaining resource sufficiency in the course of system demand growth. Major power shortages in the Midwest and California in the wake of deregulation led to a reexamination by most regions of the need for centralized resource planning and integrated resource plans. Reserve margin techniques continue to be used by many resource planners to ensure resource adequacy. Simulation-based probabilistic assessments can provide a more direct measure of adequacy but are quite intensive computationally and therefore only allow exploring a limited number of scenarios. In this paper, we suggest a simple analytical probabilistic approach to maintaining resource adequacy and calculating peak load carrying capability of incremental generating units. The methodology targets a level of system adequacy, rather than a specified reserve margin, under system expansion. It provides. a powerful technique for simply calculating probability-based load carrying capability of resource additions without iteratively running computationally intensive stochastic computer models. The technique also provides a simple but effective method for developing portfolios of resources with comparable contributions to system adequacy. The latter may be employed in capacity expansion algorithms as a simpler, more efficient, and more accurate method of determining least-cost resource additions than targeting planning reserve margins. Applications of these techniques to the IEEE Reliability Test System illustrate the methods and verify the results with a stochastic model. [ABSTRACT FROM AUTHOR]

Tens and hundreds of thousands of disturbances occur annually in modern power systems. The overwhelming majority of them are eliminated by relay protection devices and other automatic systems and by the actions of the dispatching personnel. A small fraction of the emergencies (tens of cases in such large power interconnections as those in the United States and Canada, Europe, and the United Power System (UPS) of Russia) result in significant system failures, sometimes of a cascading nature. They are consequences of unusual primary disturbances, failures of automatic emergency control systems, protection device malfunctions, and errors by personnel, but do not cause extreme consequences for the power system and the consumers. Of these, only some rare failures--blackouts--become catastrophes with severe long-term consequences for the national economies and population. Recent blackouts in North America, Europe, Russia, and other countries require specialists once again to pay closer attention to the blackout phenomenon. It is often believed that the philosophy of preventing blackouts should be based on dispatching personnel training, wide-area system visibility, and better computer models for the analysis of the stability and security of power systems. The authors of this paper also think that in emergency situations of a cascading nature, automatic emergency control systems should play a major role. A confirmation for this statement is the fact that from 1975 to 2005 there were no blackouts in the UPS of Russia (where automatic emergency control systems are widely used). At the same time, the Moscow blackout demonstrated that the growing problems in the Russia's UPS (such as aging equipment and load growth) made it also vulnerable to major blackouts. This stresses again that the electrical power industry faces common global problems and that a global effort, cooperation, and exchange of the best practices are needed to prevent blackouts. This paper describes the Russian principles and systems of dispatch and emergency control--a multilevel defense system protecting the Russian power grefid from developing cascade failures. [ABSTRACT FROM AUTHOR]

Energy storage is a natural option toward adding the much-needed flexibility for integrating higher amounts of wind generation into the existing power system. This paper presents field results and analyses quantifying the ability and the value of Sodium Sulfur (NAS) battery energy storage toward shifting wind generation from off-peak to on-peak, limiting the ramp rate of wind farm output, and a strategy to integrate the aforementioned goals. The battery can also be considered on a system level independent of wind. It is argued that even in its capacity as a system resource independent of wind, the battery can aid integration of wind generation. Analyses quantifying the value of the battery in the energy and operating reserve markets are presented. Financially optimal locations to site the battery have also been identified. The presented research is a part of the “Wind to Battery” project led by Xcel Energy, a major U.S. utility. [ABSTRACT FROM PUBLISHER]

We refer to the national infrastructure necessary to provide electric energy in the U.S. as the National Electric Energy System (NEES). It includes the three primary energy production and transportation subsystems: electric, natural gas, and coal. In order to facilitate the study of very large-scale disruptions within the NEES, we have developed a multiperiod network flow model able to simulate the movements of bulk energy flows through the network and represent large-scale disruptions on critical infrastructure. This paper describes the model with focus on special features necessary to analyze large-scale disruptions. In order to validate our approach, we have collected disruption data following the 2005 Gulf-coast Hurricanes Katrina and Rita and then incorporated these data into the model. By comparing the results with and without the hurricanes, the additional operational costs as a result of them are estimated to be $10.5 billion from September to December 2005. [ABSTRACT FROM PUBLISHER]

This paper deals with the power generation control in variable-speed wind turbines. These systems have two operation regions which depend on wind turbine tip speed ratio. A high-order sliding-mode control strategy is then proposed to ensure stability in both operation regions and to impose the ideal feedback control solution in spite of model uncertainties. This control strategy presents attractive features such as robustness to parametric uncertainties of the turbine. The proposed sliding-mode control approach has been validated on a 1.5-MW three-blade wind turbine using the National Renewable Energy Laboratory wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. Validation results show that the proposed control strategy is effective in terms of power regulation. Moreover, the sliding-mode approach is arranged so as to produce no chattering in the generated torque that could lead to increased mechanical stress because of strong torque variations. [ABSTRACT FROM AUTHOR]

This paper presents the development of a single-phase utility-interactive inverter for residential power generation to meet the specifications laid down for the 2005 Future Energy Challenge Competition sponsored by U.S. DOE and IEEE. The proposed inverter system is capable of working in both stand-alone and grid-connected mode. A control scheme for implementing both modes of operation is presented, which has simple structure with smaller number of sensors. The proposed control algorithm including the whole system control is implemented on a low cost, fixed-point DSP TM5320F2812. The experimental results from a I kW prototype show that the proposed inverter system exhibits not only low THD grid current during the grid-connected mode and well regulated inverter voltage during the stand-alone mode, but also smooth and automatic transfer between the two modes of operation. [ABSTRACT FROM AUTHOR]

The design of spot markets for generation services, such as energy, regulation, and operating reserves, and longer term markets for capacity, remain in evolution in many countries. Market design includes definition of the service, bid, or offer requirements, and rules for pricing and financial settlement. In the United States, most organized regional markets have converged on similar elements of spot market design. The design of capacity markets remains influx. Market power mitigation is currently a regulatory requirement in the United States, and experience with different methods shows that it must be carefully aligned with market design to ensure both efficient pricing and efficient investment. This paper surveys these topics and their relationships to each other and identifies researchable issues. [ABSTRACT FROM AUTHOR]

The article focuses on a competition, sponsored by the U.S. Department of Defense that aims to develop a wearable electric power system for troops. In the contest, participants are asked to design a prototype of a battery pack weighing less than 8.8 pounds and capable of powering a standard service member's equipment for 96 hours. Prizes of $1 million for first place, $500,000 for second, and $250,000 for third will be awarded to the top three teams in a demonstration under realistic conditions scheduled for fall 2008. Competitors must register by November 30, 2007 to join the program. Further, the event is open to international participation, but the individual or team leader must provide proof of U.S. citizenship.

We examine a hydrogen transition strategy of using excess electric generation capacity in the U.S. midatlantic states during off-peak hours to produce hydrogen via electrolysis. Four different generation technologies are evaluated: combined-cycle natural gas, nuclear power, clean coal, and pulverized coal. We construct hydrogen-electricity price curves for each technology and evaluate the resulting air emissions of key pollutants. Substantial capital investments may be avoided by leveraging off generation assets that would otherwise be built to produce electricity, we also account for the interaction between the production of hydrogen and wholesale electricity prices and demand. Results show that off-peak electrolysis is a plausible but not dominant strategy for hydrogen production; however, there may be a substantial real option value in using the electric power system to transition to a hydrogen economy that may exceed the direct cost savings of producing hydrogen by less expensive methods. [ABSTRACT FROM AUTHOR]

Widespread deregulation of the U.S. wholesale power industry in the late 1990s was followed in many regions by substantial overbuilding of capacity. This behavior calls in to question the longer term stability of the deregulated industry. A dynamic model structure of power-producing regions, suitable for longer term analysis of capacity investment and market stability, was created and validated against 20 years of data for two regions. Monte Carlo simulations suggest that for a realistic range of assumptions, the deregulated wholesale power markets are substantially more cyclical than they would have been under a regulated monopoly regime. The models can be improved in several areas, most notably further simplification, analysis of impacts of market structure and design, and addition of transmission constraints among regions. [ABSTRACT FROM AUTHOR]

We examine the impact of wholesale markets on operations of the bulk power system and elaborate some basic implications of engineering practices for designs of wholesale markets. This analysis is intended to provide a basis for enhancements to existing principles of engineering management. Wholesale markets bring economic and financial aspects that alter the context in which system operations are conducted, and introduce incentive and benefit--cost considerations that might alter operating procedures that previously were based on reliability considerations. The principles addressed are those relevant to the interface between engineering aspects of system operations, and economic aspects of market operations. We outline ways that engineering practices developed in the era of vertically integrated utilities might be adapted to the wholesale markets introduced since restructuring began in 1998 in the United States [ABSTRACT FROM AUTHOR]